Plasticizers are incorporated into a resin (usually a plastic or elastomer) to increase the flexibility, workability, or distensibility of the resin. The largest use of plasticizers is in the production of “plasticized” or flexible polyvinyl chloride (PVC) products. Typical uses of plasticized PVC include films, sheets, tubing, coated fabrics, wire and cable insulation and jacketing, toys, flooring materials such as vinyl sheet flooring or vinyl floor tiles, adhesives, sealants, inks, and medical products such as blood bags and tubing, and the like.
Other polymer systems that use small amounts of plasticizers include polyvinyl butyral, acrylic polymers, nylon, polyolefins, polyurethanes, and certain fluoroplastics. Plasticizers can also be used with rubber (although often these materials fall under the definition of extenders for rubber rather than plasticizers). A listing of the major plasticizers and their compatibilities with different polymer systems is provided in “Plasticizers,” A. D. Godwin, in Applied Polymer Science 21st Century, edited by C. D. Craver and C. E. Carraher, Elsevier (2000); pp. 157-175.
Plasticizers can be characterized on the basis of their chemical structure. The most important chemical class of plasticizers is phthalic acid esters, which accounted for about 85% worldwide of PVC plasticizer usage in 2002. However, in the recent past there has been an effort to decrease the use of phthalate esters as plasticizers in PVC, particularly in end uses where the product contacts food, such as bottle cap liners and sealants, medical and food films, or for medical examination gloves, blood bags, and IV delivery systems, flexible tubing, or for toys, and the like. For these and most other uses of plasticized polymer systems, however, a successful substitute for phthalate esters has heretofore not materialized.
One such suggested substitute for phthalates are esters based on cyclohexanoic acid. In the late 1990's and early 2000's, various compositions based on cyclohexanoate, cyclohexanedioates, and cyclohexanepolyoate esters were said to be useful for a range of goods from semi-rigid to highly flexible materials. See, for instance, WO 99/32427, WO 2004/046078, WO 2003/029339, WO 2004/046078, U.S. Application No. 2006-0247461, and U.S. Pat. No. 7,297,738.
Other suggested substitutes include esters based on benzoic acid (see, for instance, U.S. Pat. No. 6,740,254, and also co-pending, commonly-assigned, U.S. Provisional Patent Application No. 61/040,480, filed Mar. 28, 2008) and polyketones, such as described in U.S. Pat. No. 6,777,514; and also co-pending, commonly-assigned, U.S. patent application Ser. No. 12/058,397, filed Mar. 28, 2008. Epoxidized soybean oil, which has much longer alkyl groups (C16 to C18) has been tried as a plasticizer, but is generally used as a PVC stabilizer. Stabilizers are used in much lower concentrations than plasticizers. Copending and commonly assigned U.S. Provisional Patent Application No. 61/203,626, filed Dec. 24, 2008, discloses triglycerides with a total carbon number of the triester groups between 20 and 25, produced by esterification of glycerol with a combination of acids derived from the hydroformylation and subsequent oxidation of C3 to C9 olefins, having excellent compatibility with a wide variety of resins and that can be made with a high throughput.
U.S. Pat. No. 3,211,691, which is incorporated by reference herein in its entirety, discloses plasticized compositions comprising polymers of vinyl chloride and a tetraalkyl ester of cyclopentane 1,2,3,4-tetracarboxylic acid, wherein each of the alkyl groups contains from 3 to 12 carbon atoms, which can be derived from monohydric aliphatic alcohols including propyl alcohols, butyl alcohols, amyl alcohols, hexyl alcohols, heptyl alcohols, octyl alcohols, nonyl alcohols, decyl alcohols, undecyl alcohols, dodecyl alcohols and the like. The alkyl esters are not limited to homoalkyl esters but encompass mixed alkyl esters where one saturated aliphatic monohydric alcohol is used to esterify at least one but not more than three of the carboxyl groups in the cyclopentanetetracarboxylic acid while a different saturated aliphatic monohydric alcohol is utilized to esterify the remaining carboxyl groups.
U.S. Pat. No. 3,388,187 discloses derivatives of 1,2,3,4-cyclopentanetetracarboxylic acid having at least one unsaturated aliphatic ester moiety, suitable for cross-linking U.S. Pat. No. 3,346,598, which is incorporated by reference herein in its entirety, discloses novel esters, including tetra-esters of 1,2,3,4-cyclopentanetetracarboxylic acid useful as plasticizing agents. The alcohols used to prepare the esters contain four or more carbon atoms, and are preferably non-branched.
U.S. Pat. No. 6,355,711, which is incorporated by reference herein in its entirety, discloses a plasticizer ester prepared from the catalytic reaction of (1) at least one branched C7-C11 OXO-alcohol prepared from C6-C10 olefins with least 50% methyl branching at the beta carbon via hydroformylation, and (2) at least one acid or anhydride. Mono- and poly-basic acids are disclosed.
JP 71033933 B discloses tetraesters of butane tetracarboxylic acid wherein the ester groups are C4-C18 alkyl or C7-C18 aralkyl, which are useful as plasticizers. JP 06263915 A discloses plasticizer compositions containing a 1,2,3,4-butane tetracarboxylate wherein the ester groups are C4-C36 alkyl or alkenyl groups, such as tetraoctyl-butane tetracarboxylate, and an additional ester compound. JP 57170948 A discloses vinyl chloride resins containing 20-200 phr tetraalkyl cyclopentanetetracarboxylates, such as tetrakis(2-ethylhexyl)cyclopentanetetra-carboxylate. JP 5098106 A discloses tetraesters of butanetetracarboxylic acid as plasticizers for PVC, wherein at least one of the ester groups is cyclohexyl. JP 59022950 discloses tetraesters of butanetetracarboxylic acid having C4-C10 alkyl sidechains as plasticizers for PVC, such as n-hexyl, n-octyl, and a mixture of n-hexyl and n-octyl. PVC compositions containing the tetraesters have improved cold and evaporation resistance. JP 59118741 discloses cyclopentane-tetracarboxylic ester plasticizers, having alkyl residues of mixed carbon numbers.
To date, none of the prior art compounds or compositions has demonstrated satisfactory equivalence to conventional phthalate plasticizers for use with PVC polymers. Thus what is needed is a method of making a general purpose non-phthalate plasticizer having suitable melting or chemical and thermal stability, pour point, glass transition, increased compatibility, good performance and low temperature properties.